Downdraft Devices for Negative Emissions—Quantification Study and Environmental Implication

Methane (CH4) is a potent greenhouse gas with a global warming potential far exceeding that of CO2 over short time horizons. Its removal from the atmosphere remains challenging due to its low ambient concentration and chemical stability. This study explores downdraft energy towers (DETs) as an innovative CH4 mitigation technology that enhances the dominant hydroxyl radical (·OH) sink via water vapor release. A coupled modeling framework integrating computational fluid dynamics (CFD) and a simplified atmospheric chemistry model was developed to quantify the influence of operational parameters, environmental conditions, and tower scale. The CFD simulations evaluated internal flow dynamics and water vapor output, whereas the atmospheric model estimated ·OH production and CH4 oxidation potential. Results indicate that higher water injection rates, elevated ambient temperatures, and lower relative humidity markedly increase downdraft strength, vapor emissions, and ·OH formation. Scaling analysis showed that an 800 m${\mathrm{m}}$ DET could remove up to 141.17 t CH4 per year, with the highest efficiency in hot, dry climates. These findings highlight DETs as a promising complementary option for greenhouse gas mitigation and provide guidance for optimizing their design and deployment in climate engineering strategies.